▎ 摘　　要

We have developed metal-oxide graphene field-effect transistors (MOGFETs) on sapphire substrates working at microwave frequencies. For monolayers, we obtain a transit frequency up to similar to 80 GHz for a gate length of 200 nm and a maximum oscillation frequency of about similar to 3 GHz for this specific sample. Given the strongly reduced charge noise for nanostructures on sapphire, the high stability and high performance of this material at low temperature, our MOGFETs on sapphire are well suited for a cryogenic broadband low-noise amplifier. (C) 2011 American Institute of Physics. [doi:10.1063/1.3633105]